High-end film projector systems typically use Xe bubble lamps coupled to an ellipsoid reflector. The reflected light is captured from the first focal point of the reflector and is re-imaged at the second focal point. The second focal point is commonly co-incident with an optics component such as an integrator rod, film projector lens, etc., depending on the implementation.
Reflectors used for lamps in the 1 to 6 KW range are typically made of metal (e.g. nickel deposit) or glass. Along with reflecting visible light, the reflectors also serve the purpose of removing infrared light generated by the lamp from the second focal point. This helps in reducing the amount of heating within the projector and is vital for projector performance. With metal reflectors this is accomplished by using IR absorbing coatings at the reflector surface. IR transmitting coatings tend to be used in glass reflectors. In either case, effective cooling must be applied to the reflector and the lamp for proper operation.
To that end, air is commonly directed onto the reflector surface, either directly or by the use of ducting, to maintain the reflector temperature and temperature gradient below a predetermined threshold above which damage can occur. In most cases air is forced onto the side of the reflector and ducting is used to re-distribute the air. This often results in areas of the reflector having high temperature gradients, resulting in local distortion and reduced coupling efficiency. Typically, for metal and glass reflectors operating with 6 KW lamps, up to 800 cfm of airflow is required for effective cooling. The lamp ends and bulb also need to be cooled. When air is used to cool the reflector from the side, effective cooling occurs for one lamp end. To cool the hub, air must be forced through the back opening of the reflector, over a first end of the bulb, over the center of the bulb and finally over the opposite end. However, air flow over the opposite end is usually too low for cooling. A second fan and/or complex extra ducting from the primary fan is therefore often used to provide cooling for the opposite lamp end.
U.S. Patent No. 7,018,076 to Christie Digital Systems, Inc. teaches a compound reflector that includes an air deflector that channels a portion of the air over and outside the ellipsoid reflector, and subsequently towards the opposite end of the lamp. There remains, however, a continual need to improve upon cooling systems for use with high performance Film Projector Systems.
Ensuring cost effective and efficient cooling of the reflector for high power Xe lamps (i.e. greater than 1 KW) remains a difficult challenge to projector and cooling system designers.